This is a supplemental application designed to broaden the scope of the activities being pursued under the grant. In particular, it deals with the application of an enzyme system--plasminogen activator-- whose intracellular levels are closely correlated with oncogenic transformation, to studies of chemical carcinogenesis in cell culture and in animals. The development of procedures for more efficient carcinogenesis screening are proposed. The same procedures may be applied to isolation of cells with desired phenotypic properties. BIBLIOGRAPHIC REFERENCES: Dano, K. and Reich, E.: Inhibitors of Plasminogen Activation (1975) in Proteases and Biological Control (Reich, E., Rifkin, D.B., and Shaw, E. eds.) pp. 357-366, Cold Spring Harbor Laboratory. Jones, P., Benedict, W., Strickland, S, and Reich, E.: Fibrin Overlay Methods for the Detection of Single Transformed Cells and Colonies of Transformed Cells. Cell. 5: 323-329 (1975).